Key term
OCR GCSE Chemistry A J248
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsIonic equations, and state symbolsThe mole and the Avogadro constantConservation of mass, and changes of mass in open systemsStoichiometry, and calculating reacting massesExothermic and endothermic reactions, and reaction profilesActivation energy, and bond energy calculationsOxidation and reduction, by oxygen and by electronsAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsDilute and concentrated, weak and strongThe pH scale, and hydrogen ion concentrationpH as a factor of ten, and measuring pHProducts at the electrodes, and molten ionic compoundsElectrolysis of aqueous solutionsInert and non-inert electrodes
Elements, Compounds and Mixtures
Topic overviewPurity, and melting point dataRelative formula mass and empirical formulaeFormulations, and separating mixturesPaper and thin layer chromatographyInterpreting chromatograms and Rf valuesChoosing a purification methodMetals and non-metals in the Periodic TableElectron arrangement and position in the Periodic TableIonic, covalent and metallic bonding comparedDot and cross diagrams, and the limits of modelsReactions, electron arrangement and Mendeleev's tableCarbon's four bonds, and the variety of organic compoundsDiamond, graphite, fullerenes and grapheneBond strength, intermolecular forces and predicting stateBulk properties of ionic, molecular and giant structuresNanoparticles: size and surface area to volumeUses and risks of nanoparticulate materials
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisBiological methods of metal extractionRate against yield in industry, and reaction conditionsThe Haber process and fertiliser productionNitrogen, phosphorus and potassium in agricultureLife cycle assessmentRecycling, and the decisions behind itAlloys, and the corrosion of metalsComparing glass, ceramics, polymers, composites and metalsFunctional groups and homologous seriesPredicting the products of organic reactionsAddition polymerisationCondensation polymerisation, and making a polymerDNA and other natural polymersFractional distillation of crude oilThe fractions, and crude oil as a feedstockDependence on hydrocarbons, and crackingChemical cells and fuel cellsThe Earth's early atmosphere, and how oxygen developedThe greenhouse effect, and evidence for climate changeEffects of carbon dioxide and methane, and air pollutantsProducing potable water
Monitoring and Controlling Chemical Reactions
Topic overviewConcentration in mol/dm³, and titrationTitration calculations, and the mass of a soluteMolar gas volume and the volumes of gasesTheoretical mass and percentage yieldAtom economy, and choosing a reaction pathwayMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic equilibriumChanging the conditions of an equilibriumActivation energy, and enzymes as catalysts
Particles
Predicting and Identifying Reactions
Topic overviewGroups 1, 7 and 0, and why they behave as they doTransition metalsPredicting reactivity from the Periodic TableReactivity of metals with water and acidsTests for oxygen, hydrogen, carbon dioxide and chlorineTests for aqueous cations and anionsFlame tests, and identifying metal ionsIdentifying a species from test resultsInstrumental methods of analysis
Monitoring and Controlling Chemical Reactions
Changing the conditions of an equilibrium
- 3 things to know
- Paper 4
Overview
Le Chatelier’s principle, and the effect on the position of equilibrium of changing concentration, removing a product, raising or lowering the temperature, and changing the pressure, with the compromise conditions for ammonia and sulfur trioxide.
What you need to know
Answer each one before you reveal it.
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Key term
State the principle used to predict how the position of an equilibrium responds to a change in conditions.
Key term
Predict the effect of increasing the concentration of a reactant on the position of an equilibrium.
Questions from this subtopic
Each one with the model answer underneath.
- 1
State the principle used to predict how the position of an equilibrium responds to a change in conditions.
Model answer
Le Chatelier’s principle: if a change is made to a system at equilibrium, the position of equilibrium shifts in the direction that opposes that change.
- 2
Predict the effect of increasing the concentration of a reactant on the position of an equilibrium.
Model answer
The equilibrium shifts to the right, so more of the products are formed.
- 3
Predict the effect of continuously removing a product from an equilibrium mixture as it forms.
Model answer
The equilibrium shifts to the right to replace it, so more reactant is converted to product.
- 4
Predict the effect of raising the temperature on the position of an equilibrium.
Model answer
It shifts in the endothermic direction, because taking in energy opposes the rise in temperature.
- 5
Predict the effect of lowering the temperature on the position of an equilibrium.
Model answer
It shifts in the exothermic direction, because releasing energy opposes the fall in temperature.
- 6
Predict the effect of increasing the pressure on an equilibrium between gases.
Model answer
It shifts towards the side with the smaller number of gas molecules, because that reduces the pressure.
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